145 



TAB. CLXXVI. 



PLUMBUM sulphureum. 

 Sulphur et of Lead. 



Div. 1. Crystallized ; var. Cubo-octaedron compressed and 

 mackled. 



We have exhibited the primitive cubic crystals of this 

 substance, tab. 24. It is not rare to see the corners trun- 

 cated, which are the faces of the octaedron ; thus it passes 

 to what has been called the cubo-octaedron — see the de- 

 scription, and tab. 99. It has been lately observed, that 

 Sulphuret of Lead, or Galcena, has rarely been found in six- 

 sided tables ; and those who have the few so found, think 

 much of them on that account; and it is certainly a cu- 

 riosity, when we see a substance so decidedly fracturing in 

 cubes to find it forming the octaedron, which it often ap- 

 proaches, and sometimes does most perfectly — that a com- 

 bination of these forms should be deposited, and at the 

 same time with two of the faces much broader than the 

 rest, or other twelve; viz. six hexangular faces of the oc- 

 taedron, and six rectangular faces of the cube — see the 

 middle geometrical figure : that these should again be so 

 deposited in crystallizing, as for two to meet with two of 

 the broader faces as a basis to each, of the nature of that of 

 the mackle, tab. 33 ; and like that they will meet at oppo- 

 site angles, as if turned on an axis. Thus the six-sided 



